Electron-beam deflecting circuit



Aug. 5, 1941. R, CQMOORE 2,251,853;

ELEcTRoN-BEAM DEFLEGTING CIRCUIT.

Filed June 16, 1939 3 Sheets-.Sheet 'l fipa,

Aug. 5, 1941. R. c. MOORE ELECTRON-BEAM DEFLEGTING CIRCUIT Filed June16, 1939 3 Sheets-Sheet 2 Aug. 5, 1941.

R. c. MOORE 2,251,851

ELECTRON-BEAM DEFLECTING CIRCUIT Filed June 16, 1959 3 Sheets-Sheet 3Patented Aug. 5, 1941 ELECTRON-BEAM DEFLECTING CIRCUIT Robert C. Moore,Philadelphia, Pa., assigner, by

mesne assignments, to Philco Radio and Television Corporation,Philadelphia; Pa., a corporation of Delaware Application June 16, 1939,Serial No. 279,581v

16 Claims. (Cl. Z50-27) tion of each scan to return it toits value atthe This invention relates to electron-beam deflecting circuits of thetype employed in electronic television systems both at the transmitterwhere the television signal is generated by the scanning loi a chargeimage corresponding to the scene to be televised and at the receiverwhere the scene is reconstituted by the scanning of a uorescent screenby a beam of electrons modulated in accordance with variations in thereceived signal. More particularly, the invention relates to that methodof deecting the beam which employs a varying magnetic eld that builds upslowly at a uniform rate and decays suddenly, or vice versa.

As is well known, the scanning process at the television receiver mustbe carried out in substantially the same manner as that at thetransmitter in order that an accurate reproduction of the televisedpicture may be obtained. With this in view, it has become commonpractice to reduce the scanning process to a routine which may readilybe duplicated at the receiver to conform with that carried out at thetransmitter. The routine which has been generally adopted is one inwhich the beam is deilected so that the -point at which it impinges uponthe surface being scanned traces a series of vertically spacedsubstantially horizontal lines. Furthermore, the angular rate at whichthe scanning beam is deected both horizontally and vertically should besubstnatially uniform though the rate itself will be different in thetwo cases. Such uniform deflection is obtained by permitting theelectrons in the beam to traverse a region in which either an electricor a magnetic lield is caused to build up or to decay at a uniform rateA uniformly varying electric eld may be obtained by impressing asawtooth voltage upon the plates of a condenser While a uniformlyvarying magnetic eld may be obtained by establishing in a coil a currenthaving a sawtooth waveform. Although electric deection is generally moreconservative of energy under practical conditions than magnetic,unusually high voltages are required to obtain sufficient deflection sothat it is not generally used where large deflections are required.

Two considerations are of primary importance in the design 4of amagnetic deflecting system.

One involves the production in the deecting coil I of a uniformlyvarying current in spite of the ,presence of fortuitous circuit elementsand other rapidly in the opposite senses upon. the complebeginningthereof. A second consideration is that of power consumption whichshould be kept as low as possible, although it is inherently higher in amagnetic than in an electric deilecting system. f

Accordingly, one object of the invention is to provide a high eilciencymagnetic deflection system for use in television.

Another object of the invention is to provide a magnetic deflectionsystem for deilecting an electron beam at a substantially uniform ratethrough a given angle and for suddenly returning it to its initialposition.

Still another object of the invention is to provide a magneticdeflecting system of the type adapted to be actuated by a signalsupplied to its input in which the fundamental scanning frequency i'sdependent upon the input signal' characteristics but in which the rateof deection throughout the scan is substantially independent of theinput signal.

A further object oi. the invention is to provide automatic meansresponsive to the output signal in a. defiecting system for controllingthe amount of energy supplied to its input whereby the desired waveformobtains in the output of the system.

A still further object of the invention is to provide a means forproducing a substantially linear sawtooth current in the deecting coilof a magnetic deilecting system.

The invention will be understood clearly from the following descriptionand drawings in which:

Figs. 1, 2, and 3 are diagrammatic illustrations of differentembodiments of the invention; and

Fig. 4 shows a series of voltage and current waveforms, existing invarious parts of the systems to be described.

By way of introduction and before considering the methods and apparatusof the invention, it will be desirable to describe in some detail theoperation of a conventional deecting output system of the magnetic type.Such a system is the one of Fig. 1 omitting for the moment the resistorsil and i3, the condenser l2 and the associated connection represented bythe heavy line, which comprise (additions to the fundamental circuitmade in accordance with the principles ofthe present invention. Thenucleus of the circuit is an inductance l in which is it desired to setup the sawtooth deilecting current. This inductance may either be thedelecting coil itself or, as in the case illustrated, may be a separateinductor forming the primary of a duration of the steeper portion of thesawtooth is dependent upon the magnitude of this fortuitous capacitywhich should, therefore, be as small as possible.

In order to set up a sawtooth currentdn the inductance I, it isnecessary to impress thereacross a signal comprising abrupt peaks orimpulses. The inductance is accordingly included in the output circuitof a suitable space discharge device 6 to the input electrode of whichis supplied an impulse voltage of the form shown at 1. Although a systemsuch as described thus far may be used, it is wasteful of power sinceenergy must be supplied to the inductance throughout the entire scan.Improved efficiency is frequently obtained by connecting in shunt withthe inductance I a diode 8 which may be suitably biased by means oi thetime circuit comprising the resistor 9 and the condenser I 0, or byother suitable means, so as to limit the amplitude of the voltagedeveloped across the inductance.

It will be remembered that the resistor II is to be omitted for purposesof the present consideration. By the provision of the diode and biasingmeans, a sort of class B operation is obtained in which energy issupplied to the inductance I by the tube 6 during only the latterportion of each scanning period. When the tube is cut off at the end ofthe line by a large negative pulse applied to its grid, the energy inthe inductance I is rapidly transferred to the capacity 5, the upperplate of which assumes a positive charge with respect to ground. Whenthe charge on the condenser has reached a maximum and the current in theinductance has fallen to zero, the free oscillationcontinueswiththedischarge of the condenser to produce a current in the oppositedirection in the inductance. This continues until the condenser has beendischarged and the current in the inductance has become a maximum in theopposite direction. Were it not for the presence of the diode 8 orequivalent means, the capacity 5 would now proceed to charge in theopposite sense, since its upper plate becomes negative with respect tothe lower. developed is such as to cause the diode 8 to conduct, and thecurrent in the inductance, instead of charging the condenser, flowsthrough the return path provided by the diode 8. By reason of theresistance of the diode and its associated biasing means, the currentdecreases exponentially until all, or substantially all, of the energystored in the inductive field has been dissipated,

when the tube 6 is caused to supply energy thereto and the currentincreases.

Although the diode when properly biased serves to control the decreaseof the current in the inductance, thereby utilizing the energy suppliedtothe inductive field during the latter half of each scanning line tocontrol its operation during the rst half of the succeeding line, itsoperation is not entirely satisfactory since the current in the seriescircuit, comprising the diode, its biasing means and the inductance,tends to decrease substantially exponentially thereby producing adistorted sawtooth, Such as However, the voltage thus that indicated bythe solid line curve at D in Fig. 4. This should be compared to thedesired sawtooth wave iorm shown at A in Fig. 4, which requires that thevoltage on the plate of the tube E vary as shown at B in Fig. 4.

It follows that the voltage across the inductance must be the vectordifference between the plate supply voltage and the voltage on the plateof the tube itself, which is approximated by the wave represented by thesolid line at C. In the absence of the diode, the oscillation whichtakes place in the circuit comprising the inductance I and the capacity5 during the time the tube 5 is cut od. would tend to overshoot thelevel portion of the solid line curve as indicated by the broken linecurve. By using the biased diode or its equivalent, this tendency tooverswing at the end of the return time is avoided. The net result is acurrent in the inductance which is substantially as shown by the solidline curve at D in Fig. 4. If the deiiection is to be linear, this mustbe modified so as to conform with the dotted lines in the same figure. j

Considering now the diode current when the system is operating asdescribed above, it will be found to vary substantially as representedby the curve E of Fig. 4. In order to obtain the desired linear sawtoothcurrent in .the inductance I, this should be modified to conform withthatrepresented by the solid line curve F of Fig. 4, or additional meansshould be provided so that the total current in the inductance duringthe first half of each scanning line varies in this manner. This mightbe accomplished by varying the series resistance of the circuitcomprising the diode, its biasing means, and the inductance, so as toobtain the desired current waveform. This woulid obtain if the seriesresistance were to be increased linearly duringthe first half of eachscanning line.

In accordance with the present invention, however, it is proposed topermit the driver or output tube 6 to draw current in an amountsuiiicient to supply the'difference between the diode current and thatdesired in the inductance. Ac-

cordingly, the series resistance of the diode circuit might be adjustedso that the initial slope of the corresponding curve of current decay.therein will be equal to the desired slope of the sawtooth current, asindicated by the dotted curves at I" in Fig. 4. The driver tube may thenbe controlled so as to supply the required complementary current duringthe rs't half of the scanning cycle and so as to increase insubstantially linear fashion during the latter half of the cycle. 'I'hedesired wave of currentl in the tube 6 may accordingly be of the formshown at G in Fig. 4. Although the current in the tube 6 may be thuscontrolled by the application of a suitable control signal to the gridof tube 6 from some external source, it has been found that the desiredcontrol may be obtained from the output circuit itself. This method isparticularly advantageoussin'ce it makes the output self-regulatory andindependent of any of the idiosyncrasies of the usual deiiecting signalgenerators, which are attributable to failure to synchronize as well asto properties of the. circuits themselves. The present method obviatesthese difficulties so that the Waveform of the deiiecting coil currentis automatically self-controlled, only the beginning and end points ofeach scanning line being dependent upon the externally suppliedsynchronizing signal.

In the embodiment of Fig. 1, a control voltage current in the inductancemay be controlled by may be derived across a resistor II included in thediode circuit. This is fed back to the input circuit of the tube 8 bythe heavy-line connection which includes the blocking condenser I2. Theresistor Il must necessarily be relatively small in order not tointerfere wtih the normal and de-,`-

sired operation ot the diode B, and hence in order not disadvantageouslyto increase the load upon the signal source, it may be necessary tointroduce the resistor I3 in the connection. The magnitude oi this will,of course, be chosen with a view to the effective internal impedance ofthe source applying signal to the tube 6. Nowfit will be noted thatearly in the scanning period, when the diode current is large, anappreciable negative voltage will develop across the resistor Il. Thiswill tend to cut oif the tube 8. As the current in the diode circuitdecays, the resistor voltage decreases thereby decreasing the bias onthe tube 6 which, if the fixed bias provided by the combination of theresistor il and the condenser i5 is of a suitable value. may be causedto draw the required complementary current to give a current wave-formas shown at I6 in the inductance i. The bias developed acrosstheresistor ii may vary as indicated at i'I throughout the scan, from whichit appears that no control would be exercised during the latter part ofthe scan, and this may indeed be the case provided that the input signal"i is substantially constant throughout. However, if this is not thecase and the input signal swings excessively positive at any time, thevoltage developed across the inductance i by the more than linearincrease in current therethrough will cause the cathode of the diode toswing more negative with respect to its plate. Consequently, diodecurrent will ow and the bias thereby developed, when supplied to thegrid of the tube t will compensate for the variation in the input signaland will restore equilibrium in the output. This' restoring force, itshould be noted, will be developed Whenever during the scanningperiod-the current in the inductance (l tends to increase at too great arate, and adequately compensates for any changes in the input signal. Ingeneral then, the only characteristic which this signal must possess isa relatively well defined negative peak sufficient to insure cut off ofthe tube ti throughout the entire return time. The end of each scanningcycle and the beginning of the next cycle will depend upon the time ofoccurrence oi these peaks, but otherwise the operation of the circuitWill be substantially independent of the form of the input signal. Thiswill, of course, permit the obtaining of the de sired uniform deflectionof an electron beam in a television picture tube or like device.

It has been observed that it is not feasible to make the resistor iiunduly large, which may place a limitation upon the available bias forcontrolling the tube One Way of obviating this diiiculty is by the useof an additional diode, as shown in the embodiment ofFig. 2. Here thediode t carries the major part of the current from the inductance i andhas no resistance in series with it, other than that of the biasingmeans. The bias voltage is derived across a relatively larger resistorii than the one used in the previous embodiment,l which is connected inseries with the additional diode i8. This avoids any loadingdiiilculties which might otherwise obtain, while giving the desiredcontrol in substantially the same manner as-heretofore described.

As has already been noted, the ldecay of the varying theI resistance inthe diode circuit in a suitable manner. This may be effected, as shownin Fig. 3, by substituting for the diode an inverted triode or a tetrodeI9. In order to obtain the desired sawtooth current, the resistanceshould be increased uniformly which 'may be accomplished by applying asawtnoth voltage to the'controi grid of the tube I9. Since impulsevoltage is available on the plate of the tube 6, a sawtooth voltage maybe obtained by applying the impulse voltage across a series combinationcomprising a resistor 20 and a condenser 2 I. The condenser voltage willthen correspond to the solid'curve 22. The voltage drop across theresistor 20 will -accordingly be the difference between the voltage onthe plate of the tube 6 and that across the condenser which, measuredwith respect to the plate of the tube, corresponds to the dotted curve23. This is such as to give the desired resistance variation whenapplied to the grid of the tube I9.

This mode of controlling the current in the inductance'i should, ofcourse, give the desired waveform therein provided that the propersignal is applied to the input of the tube il. However, sinceI it isdesirable that the current in the coil i should be independent of theinput signal to as great a degree as is possible, the method of theinvention may be advantageously employed in this case also. Accordingly,the resistor ii is provided in the plate circuit of the tube iii, i'romwhich bias voltage may be derived and fed back through the condenser 2liwhich by-passes the D. C. plate voltage dropping resistor 25. In thiscase, the control is applied to the screen grid of the tube t. It will,of course, be understood that the bias voltage may be aplplied in anysuitable manner to controlthe driver tube. In the case where the sourceof external signal to be applied to the grid of the tube is a gasdischarge tube oscillator or similar device Whosel operation isdeleteriously affected by the variation in plate voltage which the biasmay produce, it is desirable to apply the bias in some way which willnot so affect it. One such method is by applying the bias to the screengrid, as here shown. Another method is to apply the bias across aresistor in the cathode circuit of the gas tube oscillator whereby theentire oscillator circuit fioats up and down on the bias voltage butthere is no appreciable effect upon its synchronizatori.

From the above explanation of the principles of the invention it will beclear to those skilled in the art that there are numerous extensions ofthe principles within the scope of the invention. Thus the inventionshould not be regarded as limited to the specific embodiments shown butis rather defined by the scope of the appended claims.

I claim:

l. In an electron beam deiiecting system wherein a magnetic field isvaried to deect electrons passing therethrough; means responsive toelecy trical energy supplied thereto from an external source forestablishing a varying magnetic field; means coupled to said last meansfor removing energy'from said field, when the strength of said eldreaches a maximum in a particular sense, for storing said energy and forreturning it to said field so as to build up said field in the oppo-lsite sense; means for controllably dis'sipating the energy contained insaid field when it is of said opposite sense; and means for controllingthe amount and sense of the energy supplied to said field from saidexternal source in accordance with the rate at which said energy iscontrollably dissipated.

2. In an electron beam deilecting system, in ductive means adapted toset up a varying magnetic field in response to a current producedtherein; controllable means for altering the current in said inductivemeans; means adapted to store the energy contained in said magnetic ieidand to effect a reversal of the current in said inductive means when thesaid current has ceased to be changed by the operation of said secondmeans; means connected in shunt with said inductive means and adapted toconduct whenever the current therethrough` tends to increase at greaterthan a predetermined rate; and means responsive to the current in saidlast means for controlling the current alteration in said inductivemeans by said second means in accordance with the current in said lastmeans.

3. In an electron beam deflecting device employing magnetic deflectingmeans; a resonant circuit comprising the inductance and distributedcapacitance of said magnetic deiiecting means; controllable means forsupplying energy to and removing energy from said resonant circuit; adiode and a serially connected biasing means connected across saidresonant circuit; and means responsive to the current in said diode forcontrolling the energy transfer between said energy supply means andsaid resonant circuit.

4. In an electron beam defiecting device employing magnetic deectingmeans; a resonant circuit including the inductance of said deflectingmeans; a source of a signal adapted to excite said resonant circuit;means for supplying said signal to said resonant circuit; meansconnected in shunt with said resonant circuit and adapted to conductwhenever the voltage across the said resonant circuit exceeds apredetermined value; means for deriving a signal proportional to thecurrent in said last mentioned means; and means for applying saidderived signal so as to modify the signal supplied to said resonantcircuit from said source.

5. In an electron beam deecting system; means supplied with electricalenergy for establishing1 a periodically varying electromagnetic eld in aregion traversed by the electrons of said beam; controllable meansadapted to supply energy to said iirst means during a part of each cycleand capable of dissipating energy therefrom during a different part oi?the cycle; means coupled to said rst means and adapted to remove energytherefrom and to store it during a part of the cycle and to return saidenergy thereto during another part of the cycle; means connected to saidrst means for dissipating energy therefrom during a part of the cycle;and means for controlling the amount of energy supplied or dissipated bysaid second means in accordance with the rate of which energy isdissipated by said last-named means.

6. In an electron beam deflecting device employing magnetic deilectingmeans; a resonant circuit comprising the inductance and distributedcapacitance of said magnetic deiiecting means; controllable means forsupplying energy to and removing energy from said resonant circuit; aserially connected diode, impedance, and biasing means connected inshunt with said resonant circuit; and means for applying the vvolt-- agedeveloped across said impedance to control the energy transfer betweensaid energy supply means and said resonant circuit. '1

'7. In an electron beam deilecting device employing magnetic deiiectingmeans; a resonant circuit comprising the inductance and distributedcapacitance of said magnetic deecting means; controllable means forsupplying energy to and removing energy from said resonant circuit; adiode and a serially connected biasing means connected in shunt withsaid resonant circuit; a second diode and a serially connected impedancealso connected in shunt'with said resonant circuit; and means forapplying the voltage developed across said impedance to control theenergy transfer between said energy supply means and said resonantcircuit.

8. In a electron beam deflecting system; in-

ductive means adapted to set up a varying magnetic field in response toa current produced therein; controllable means for altering the currentin said inductive means; means adapted to store the energy contained insaid magnetic field and to eiiect a reversal of the current in saidinductive means when the said current has ceased to be changed by theoperation of said second means; a space discharge device having a Workcircuit and a control circuit, and having its work circuit coupled tosaid inductive means; means for controlling the current in said workcircuit so as to cause the current in said inductive means to decreaseat a substantially uniform rate; and means responsive to the current insaid work circuit for controlling the alteration in the current in saidinductive means by the said second means.

9. In an electron beam deecting system, inductive means adapted to setup a varying magnetic field in response to a current produced therein, acircuit including a space discharge device connected to said inductivemeans, control means including another space discharge device connectedto said circuit, a source of control signals connected to said otherspace discharge device, means for deriving a control voltage from saidcircuit, and means for applying said control voltage to said other spacedischarge device to controllably bias the same.

l0. In an electron beam deflecting system, inductive means adapted toset up a varying magnetic field in response to a current producedtherein, a circuit connected to said inductive means, said circuitincluding serially a space discharge device, biasing means therefor, andan impedance, control means including another space discharge deviceconnected to said circuit, a source of control signals connected to saidother space disharge device, means for deriving a control voltage fromsaid impedance, and means for applying said control voltage to saidother space discharge device to controllably bias the same.

l1. In an electron beam deflecting system, inductive means adapted toset up a varying magnetic eld in response to a current produced therein,a non-linear device in shunt with said inductive means for controllingthe current therein, signal responsive means including a space dischargedevice connected to said inductive means and said shunt means, a sourceof control signals connected to said space discharge device, means forderiving a control voltage from the current in said non-linear device,and means for applying said control voltage .to said space dischargedevice to controllably bias the same.

l2. In an electron beam deiiecting system, an electron discharge devicehaving at least a control grid, a cathode and an anode, a source ofsignals connected to the grid-cathode circuit of said device, aninductance connected to the anode-cathode circuit of said device forproducing a varyingl magnetic iield in response to said signals, anon-linear device in shunt with said inductance for controlling thecurrent therein, means for deriving a control voltage from the currentin said non-linear' device, and means for 'applying said control voltageto said electron discharge device to controllably bias the same.

13. In an electron beam deilecting system; a series circuit comprisinga. source of electrical energy, inductive means adapted to set up avarying magnetic eld in response to a current produced therein, andcontrollable impedance means for regulating the ilow of current in saidseries circuit; a source of a control signal; means for applying saidsignal to said impedance to control the same; space discharge meansshunting said inductive means; means for deriving a control voltagedependent upon the current in said space discharge means; and means i'orapplying said voltage to said impedance means to further control the.same.

14. In an electron beam deilecting system; a series circuit comprising asource of electrical energy, inductive means adapted to set up avarying/magnetic iield in response to a current produced therein, andcontrollable impedance means i'or regulating the flow of current in saidseries circuit; a source of control signal; means for applying saidsignal to said impedance to control the same; a second controllableimpedance means shunting said inductive means; means for controlling theimpedance of said second impedance means in response to thevoltagedeveloped across l said inductive means; means for deriving acontrol voltage dependent upon the current in said second controllableimpedance means; and means for applying said voltage to said firstimpedance means to further control the same.

15. In an electron beam defiecting system; a space discharge devicehaving at least an anode, a cathode, and a control grid; an inductanceconnected in the anode circuit of said space discharge device; a circuitcomprising a serially connected diode and an impedance element connectedin shunt with said inductance; a connection from the junction of saiddiode and said impedance element to the grid of said space dischargedevice; and a source of a controlling signal connected to the grid ofsaid space discharge device.

16. In an electron beam deilecting system; a space discharge devicehaving at least an anode, a cathode, and a plurality of controllingelectrodes interposed between said cahtode and said anode; an inductanceconnected in the anode circuit of said space discharge device; a circuitconnected in shunt with said inductance, said circuit including a triodespace discharge device and an impedance element; a connection from thejunction of said triode space discharge device and said impedanceelement to one of said. controlling electrodes; and a source of acontrolling signal connected to the one of said controlling electrodes.

ROBERT C. MOORE.

